1. Field of the Invention
The present invention relates to a voltage-controlled oscillator constituting a local oscillator used in a mobile communication unit, such as a portable telephone. The present invention also relates to a method for making such a voltage-controlled oscillator.
2. Description of the Related Art
The configuration of a conventional voltage-controlled oscillator will be described below by referring to FIG. 5.
In FIG. 5, there is shown a substrate 21 for a voltage-controlled oscillator. A plurality of ceramic sheets are laminated to form the substrate 21. On one main surface 21a of the substrate 21, circuit devices such as a varicap diode Vd serving as a variable-capacitance device, a capacitor C1, and a transistor Tr are provided. At side faces 21c and 21d of the substrate 21, generally semicircular indentations 24a, 24b, 24c, and 24d, and generally elongated-circular indentations 25a and 25b having a larger opening than the indentations 24a to 24d are formed. At side faces 21e and 21f, generally elongated-circular indentations 25c and 25d are formed in the same way as for the indentations 25a and 25b. A conductive member is applied to the inner surfaces of these indentations to form input terminals, a power voltage terminal Vb, a voltage control terminal Vc, a modulation terminal M1, an output terminal P1, and ground terminals Ga, Gb, Gc, and Gd. The circuit devices, the input terminals, the output terminal, and the ground terminals are connected to each other through wiring sections (not shown) formed on one main surface 21a of and inside the substrate 21. A control voltage applied to the voltage control terminal Vc, which is an input terminal, is changed to alter the capacitance of the varicap diode Vd, thereby changing the oscillating frequency. A control voltage applied to the modulation terminal M1, which is also an input terminal, is changed to start and stop oscillation.
A manufacturing method for the conventional voltage-controlled oscillator will be described next.
A motherboard 31 shown in FIG. 6 is prepared first. More specifically, in constructing the motherboard, a conductive member is printed on or applied to a plurality of ceramic sheets (not shown). Then, circuit devices and wiring sections are provided. These sheets are then laminated to form the motherboard 31. The motherboard 31 is cut along boundaries 33a and 33b to produce a number of the individual substrates 21 shown in FIG. 5.
More specifically, in the motherboard 31, through holes 34 having generally elongated-circular openings are provided on the boundaries 33a, and through holes 35 having generally circular openings and through holes 34 are provided on the boundaries 33b. A conductive member (not shown) is applied to the inner surfaces of the through holes 34 and 35. The motherboard 31 is cut along the boundaries 33a and 33b to produce a plurality of the substrates 21. In this case, the through holes 34 and 35 are divided and the conductive member applied to the inner surfaces of the through holes 34 and 35 are exposed to form the input terminals Vb, Vc, and M1, the output terminal P1, and the ground terminals Ga to Gd of the substrate 21. Each substrate 21 obtained in this way is put in a metal case (not shown) for shielding to form a voltage-controlled oscillator.
In the conventional voltage-controlled oscillator, however, since each terminal is provided on a side face of the substrate 21, the distance between the output terminal P1 and the power voltage terminal Vb and the voltage control terminal Vc becomes short. Therefore, radiation may occur between these terminals due to high-frequency interference, and, as a result, phase-noise (C/N) characteristics may deteriorate.
In the conventional manufacturing method for a voltage-controlled oscillator, since the through holes 35 formed on the motherboard 31 are shared by two divisions (substrates 21) specified by the boundaries 33b, which are used as input and output terminals, it is necessary to form a relatively large number of the holes in the entire motherboard 31. In addition, since the diameter of the holes is small, making the holes is complicated, which makes cost reduction difficult.